This invention relates to an apparatus and method for controlling a washing machine. More particularly, this invention relates to a washing machine control apparatus using an combination of a timer automatically controlling the steps of washing, rinsing and dehydrating by a washing machine and a control circuit controlling a drive motor, and relates also to method for controlling the washing machine.
A mechanical timer was used hitherto so as to control the washing, rinsing, dehydrating and other operations of a washing machine, and these operations of the washing machine were sequentially controlled by cam switches actuated by the operation of the timer.
JP-A-55-19130, JP-A-55-106196, etc. propose improvements in which such a mechanical timer is replaced by a microcomputer as so to attain a higher grade control for the washing machine. Also, JP-A-56-102290 proposes a washing machine control apparatus in which a controller is used so as to change the operating speed of the mechanical timer.
Further, JP-A-58-105793 proposes another washing machine control apparatus. In this washing machine control apparatus, a semiconductor switch, which is connected in series with a timer having a contact turned on by manual setting and an associated timing cam, is used to control a drive motor. This semiconductor switch operates in accordance with the period of oscillation of an oscillation circuit.
It is a common practice in a washing machine that its drive motor is turned on-off or rotated in normal and reverse directions as to adjust the flow of water. Therefore, in order to more finely adjust the flow of water, it is necessary to turn on-off the drive motor with shortened on-off timing.
In the case of the related art washing machine using the mechanical timer, an attempt to attain the fine adjustment of the flow of water by increasing the number of the cam switches in the timer thereby turning on-off the drive motor with shortened on-off timing cannot achieve the desired accuracy of on-off timing. Therefore, it is difficult to attain the desired fine adjustment of the flow of water. Further, the shortened timing of turning on-off the cam switches may lower the reliability of contact arms and contacts of the cam switches. Also, each time the cam switches are turned on-off, undesirable switch noise will be generated due to the opening and closing of the contacts.
In the related art washing machine using the microcomputer for the purpose of operation control, a control circuit as shown in FIG. 6 is employed. In the control circuit shown in FIG. 6, a control circuit board 67 provided for controlling the washing machine is normally kept connected to a power source unless a power supply switch 64 is turned off, and this arrangement leads to the possibility of mis-operation due to, for example, external noise. Also, the above arrangement has such another problem that, once the mis-operation takes place, the control circuit will not be reset unless the power supply switch 64 is turned off.
Also, in the washing machine control apparatus disclosed in JP-A-58-105793, no consideration is given for the combination of the timer and a control circuit for controlling the series of the steps of washing, rinsing and dehydrating. Thus, the disclosed control apparatus is defective in that the operation of the drive motor cannot be finely controlled for each of the individual steps.